[FOLLOWUP] Simplify Composer extension test setups

The root package is now always considered as TYPO3 package.
The "ignore-as-root" flag and the exclusion of root packages
in general was only introduced to allow integration testing
setups of extensions with public resources.

For such a scenario to work properly, the testing framework
introduced \TYPO3\TestingFramework\Composer\ExtensionTestEnvironment
to be included as composer autoload hook, which symlinks
the root path inside the typo3conf/ext folder.

This exact behaviour is now introduced in TYPO3 directly,
making it possible to always consider the root package for TYPO3,
and obsoleting the double negative "ignore-as-root" flag.

Releases: master
Relates: #94996
Change-Id: Ib033b7634736f5f201b55ad374943cb10dafa0a6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71029


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>